Take Rogero or Rebug... Either of them is brilliant. Rogero has had some revisions and has become stable. Rebug is... well, everyone loved Rebug on 3.55, because of their wellmade proff. firmware, and that feeling hasn't changed with 4.21. I have heard of no bricks with rebug whatsoever.
I don't believe I will hear of any of that with Rogero's anymore though..
Imo ,they are equally well. And the difference between 4.21 and 4.31 should mean NOTHING to you. The keys havent changed so if you use rebug 4.21, multiman will ask you if it should change the .sfo on the fly...
Really, roll the dices and just choose one of them unless you need DEX features. Both come from immensely skilled people.